Wide-angle zoom lens system

ABSTRACT

A wide-angle zoom lens system includes a negative first lens group, a positive second lens group, a positive third lens group, a negative fourth lens group, and a positive fifth lens group. Upon zooming from the short to the long focal length extremities, the first lens group moves toward the image and thereafter moves toward the object, the distance between the first and second lens group decreases, the distance between the second and third lens groups decreases, the distance between the third and fourth lens groups increases, and the distance between the fourth and fifth lens groups decreases.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wide-angle zoom lens system which hasa large-angle-of-view at the short focal length extremity, and which issuitable for a photographing lens system in a camera or a movie camera,etc.

2. Description of the Prior Art

In the prior art, as a zoom lens system attempting to achieve a widerangle-of-view at the short focal length extremity, such a zoom lenssystem has been disclosed, for example, in Japanese Unexamined PatentPublication (hereinafter, JUPP) No.2000-131611. However, in JUPP No.2000-131611, the half angle-of-view at the short focal length extremityis 48γ, so that the wide angle-of-view is not sufficiently achieved atthe short focal length extremity.

Furthermore, in JUPP No.2002-242336, proposed by the inventor of thepresent invention, the angle-of-view at the short focal length extremityhas been made wider than that of JUPP No. 2000-131611; however, the zoomratio is approximately 2. Therefore a higher zoom ratio has yet beenrequired.

Still further, in the case of a wide-angle zoom lens system of afive-lens-group arrangement like the zoom lens system of the presentinvention, such a wide-angle zoom lens system has been proposed in,e.g., JUPP Nos. Hei-7-306362, Hei-9-0.230242, and 2000-292701.

In JUPP No. Hei-7-306362, the zoom ratio is as high as 3.75; however,the angle-of-view at the short focal length extremity is notsufficiently larger.

In JUPP No. Hei-9-230242, the zoom ratio is 2.75, which is also high;however, the angle-of-view at the short focal length extremity is notsufficiently larger.

The zoom lens system, disclosed in JUPP No. 2000-292701, is to be usedin a projector; and the angle-of-view at the short focal lengthextremity is not sufficiently larger. Moreover, the overall length ofthe zoom lens system is fixed (not variable), and is not suitable for aphotographing lens to which miniaturization is required for portability.

SUMMARY OF THE INVENTION

The present invention provides a wide-angle zoom lens system in which(i) the angle-of-view of at the short focal length extremity is morethan 100γ, (ii) a zoom ratio is approximately 2.9, and (iii) thediameter of lens elements is smaller.

According to an aspect of the present invention, there is provided awide-angle zoom lens system including a first lens group having anegative refractive power (hereinafter, a negative first lens group), asecond lens group having a positive refractive power (hereinafter, apositive second lens group), a third lens group having a positiverefractive power (hereinafter, a positive third lens group), a fourthlens group having a negative refractive power (hereinafter, a negativefourth lens group), and a fifth lens group having a positive refractivepower (hereinafter, a positive fifth lens group), in this order from theobject.

Upon zooming from the short focal length extremity to the long focallength extremity, the negative first lens group first moves toward theimage and thereafter moves toward the object; the distance between thenegative first lens group and the positive second lens group decreases,the distance between the positive second lens group and the positivethird lens group decreases, the distance between the positive third lensgroup and the negative fourth lens group increases, and the distancebetween the negative fourth lens group and the positive fifth lens groupdecreases.

The wide-angle zoom lens system satisfies the following condition:0.3<dL ₁₋₂ /d ₂₋₃<5.0  (1)

-   -   wherein    -   dL₁₋₂ designates the difference in the distance between the        negative first lens group and the positive second lens group at        the short focal length extremity and the distance therebetween        at the long focal length extremity; and    -   dL₂₋₃ designates the difference in the distance between the        positive second lens group and the positive third lens group at        the short focal length extremity and the distance therebetween        at the long focal length extremity.

The wide-angle zoom lens system preferably satisfies the followingcondition:2.1<(L ₁₋₂ +L ₂₋₃)/fw<5.5  (2)

-   -   wherein    -   L₁₋₂ designates the distance between the negative first lens        group and the positive second lens group at the short focal        length extremity;    -   L₂₋₃ designates the distance between the positive second lens        group and the positive third lens group at the short focal        length extremity; and    -   fw designates the focal length of the entire wide-angle zoom        lens system at the short focal length extremity.

If an attempt is made to integrally move the positive third lens groupand the positive fifth lens group upon zooming, the mechanism of thewide-angle zoom lens system can easily be established.

The wide-angle zoom lens system can satisfy the following condition:1.7<d _(X3) /fw<4.0  (3)whereind_(X3) designates the traveling distance of the positive third lensgroup from the short focal length extremity to the long focal lengthextremity. Note that the direction toward the object is defined as thepositive direction.

If an attempt is made to linearly move the positive third lens group andthe negative fourth lens group upon zooming, the mechanism of thewide-angle zoom lens system can easily be established.

The negative first lens group preferably includes a negative firstmeniscus lens element having the convex surface facing toward theobject, a negative second meniscus lens element having the convexsurface facing toward the object, and a third meniscus lens elementhaving the convex surface facing toward the object, in this order fromthe object. The third meniscus lens element is made of resin.

The negative first lens group satisfies the following condition:|f1/f _(L3)|<0.2  (4)

-   -   wherein    -   f1 designates the focal length of the negative first lens group;        and    -   f_(L3) designates the focal length of the third meniscus lens        element in the negative first lens group.

The wide-angle zoom lens system preferably satisfies the followingcondition:0.2<fw/f3<0.9  (5)

-   -   wherein    -   f3 designates the focal length of the positive third lens group.

The wide-angle zoom lens system preferably satisfies the followingcondition:−0.6<fw/f4<−0.1  (6)

-   -   wherein    -   f4 designates the focal length of the negative fourth lens        group.

The present disclosure relates to subject matter contained in JapanesePatent Application No.2003-027946 (filed on Feb. 5, 2003) which isexpressly incorporated herein in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity, according to a first embodiment of thepresent invention;

FIGS. 2A, 2B, 2C, 2D and 2E show aberrations occurred in the lensarrangement shown in FIG. 1;

FIGS. 3A, 3B, 3C, 3D and 3E show aberrations occurred in the lensarrangement shown in FIG. 1 at an intermediate focal length on the sideof the shorter focal length;

FIGS. 4A, 4B, 4C, 4D and 4E show aberrations occurred in the lensarrangement shown in FIG. 1 at an intermediate focal length on the sideof the longer focal length;

FIGS. 5A, 5B, 5C, 5D and 5E show aberrations occurred in the lensarrangement shown in FIG. 1 at the long focal length extremity;

FIG. 6 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity, according to a second embodiment of thepresent invention;

FIGS. 7A, 7B, 7C, 7D and 7E show aberrations occurred in the lensarrangement shown in FIG. 6; FIGS. 8A, BB, 8C, 8D and 8E showaberrations occurred in the lens arrangement shown in FIG. 6 at anintermediate focal length on the side of the shorter focal length;

FIGS. 9A, 9B, 9C, 9D and 9E show aberrations occurred in the lensarrangement shown in FIG. 6 at an intermediate focal length on the sideof the longer focal length;

FIGS. 10A, 10B, 10C, 10D and 10E show aberrations occurred in the lensarrangement shown in FIG. 6 at the long focal length extremity;

FIG. 11 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity, according to a third embodiment of thepresent invention;

FIGS. 12A, 12B, 12C, 12D and 12E show aberrations occurred in the lensarrangement shown in FIG. 11;

FIGS. 13A, 13B, 13C, 13D and 13E show aberrations occurred in the lensarrangement shown in FIG. 11 at an intermediate focal length on the sideof the shorter focal length;

FIGS. 14A, 14B, 14C, 14D and 14E show aberrations occurred in the lensarrangement shown in FIG. 11 at an intermediate focal length on the sideof the longer focal length;

-   -   Figures ISA, 15B, 15C, 15D and 15E show aberrations occurred in        the lens arrangement shown in FIG. 11 at the long focal length        extremity;

FIG. 16 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity, according to a fourth embodiment of thepresent invention;

FIGS. 17A, 17B, 17C, 17D and 17E show aberrations occurred in the lensarrangement shown in FIG. 16;

FIGS. 18A, 18B, 18C, 18D and 18E show aberrations occurred in the lensarrangement shown in FIG. 16 at an intermediate focal length on the sideof the shorter focal length;

FIGS. 19A, 19B, 19C, 19D and 19E show aberrations occurred in the lensarrangement shown in FIG. 16 at an intermediate focal length on the sideof the longer focal length; and

FIGS. 20A, 20B, 20C, 20D and 20E show aberrations occurred in the lensarrangement shown in FIG. 16 at the long focal length extremity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the embodiments of FIGS. 1, 6, 11 and 16, the wide-anglezoom lens system according to the present invention includes a negativefirst lens group 10, a positive second lens group 20, a positive thirdlens group 30, a negative fourth lens group 40 and a positive fifth lensgroup 50, in this order from the object.

As shown in the lower portion in each of FIGS. 1, 6, 11 and 16, uponzooming from the short focal length extremity (S) to the long focallength extremity (L), the negative first lens group 10 first movestoward the image and then moves toward the object; the distance betweenthe negative first lens group 10 and the positive second lens group 20decreases, the distance between the positive second lens group 20 andthe positive third lens group 30 decreases, the distance between thepositive third lens group 30 and the negative fourth lens group 40increases, and the distance between the negative fourth lens group 40and the positive fifth lens group 50 decreases.

A diaphragm S is provided in front of the positive third lens group 30(on the object side), and moves together with the positive third lensgroup 30.

In a photographing optical system utilized in an SLR camera, a videocamera, or a digital still camera, etc., if an attempt is made toachieve a zoom lens system in which the angle-of-view at the short focallength extremity is larger, it is common practice to distribute therefractive power in the zoom lens system so that the negative refractivepower is given to a front lens group (a lens group on the side of theobject: a negative-precede type) and the positive refractive power isgiven to a rear lens group (a lens group on the side of the image) forthe purpose of securing a space (i.e., providing a long back focaldistance) for filters, a quick-return mirror, or a prism on the side ofthe image plane.

In order to largely increase the zoom ratio of the abovenegative-precede type wide-angle zoom lens system, there is a need tosecure a longer traveling distance of the subsequent (positive) rearlens group. On the other hand, it should be noted that a mere increaseof the traveling distance thereof makes the height of off-axis lightrays passing through the peripheral portion of the (negative) front lensgroup higher, as the angle-of-view at the short focal length extremitybecomes larger. Consequently, the diameter of the (negative) front lensgroup becomes larger. Moreover, a filter is usually mounted immediatelyin front of the photographing lens system. As a result, an increase ofthe diameter of the (negative) front lens group inevitably makes eventhe size of an accessory, such as a filter, larger.

Accordingly, in the present invention, in order to reduce the diameterof the negative first lens group 10 (the front lens group), a positivelens group (the second lens group 20) is provided between the negativefirst lens group 10 and the subsequent positive lens group (i.e., thecombination of the positive third lens group 30, the negative fourthlens group 40, and the positive fifth lens group 50), so that the heightof the off-axis light rays passing through the negative first lens group10 is reduced.

Condition (1) is for appropriately positioning the positive second lensgroup 20 at the short focal length extremity and the long focal lengthextremity, respectively.

If dL₁₋₂/dL_(2')exceeds the lower limit of condition (1), the height ofthe off-axis light rays passing through the negative first lens group 10becomes too low, so that peripheral illumination cannot be secured.

If dL₁₋₂/dL_(2')exceeds the upper limit of condition (1), the amount ofperipheral illumination increases; however, the height of the off-axislight rays passing through the negative first lens group 10 becomeshigher. Consequently, the diameter of the negative first lens group 10cannot be made smaller.

Condition (2) specifies the sum of the distance between the negativefirst lens group 10 and the positive second lens group 20, and thedistance between the positive second lens group 20 and the positivethird lens group 30, and indirectly secures the traveling distances ofthe lens groups behind the positive third lens groups 30.

If the sum of the above-mentioned distances becomes smaller to theextent that (L₁₋₂+L₂₋₃/fw exceeds the lower limit of condition (2), thetraveling distances of the lens groups behind the positive third lensgroup 30 cannot be secured. As a result, an adequate zoom ratio cannotbe secured.

If the sum of the above-mentioned distances becomes larger to the extentthat (L₁₋₂+L₂₋₃/fw exceeds the upper limit of condition (2), thetraveling distances of the lens groups behind the positive third lensgroup 30 can be secured. However, the overall length of the wide-anglezoom lens system becomes longer, and peripheral illumination cannot besecured.

Condition (3) specifies the traveling distance of the positive thirdlens group 30 for the purpose of achieving a higher zoom ratio. Moreconcretely, Condition (3) is to specify the traveling distance of thepositive third lens group 30 under the condition that the positive thirdlens group 30 is considered to be the most object-side lens group in theabove-mentioned subsequent positive lens group(i.e., the combination ofthe positive third lens group 30, the negative fourth lens group 40, andthe positive fifth lens group 50).

If the traveling distance of the positive third lens group 30 becomesshorter to the extent that d_(X3)/fw exceeds the lower limit ofcondition (3), the refractive power of the positive third lens group 30to the positive fifth lens group 50 has to be made stronger for securingthe zoom ratio. Consequently, aberrations increase, and opticalperformance cannot be maintained.

If the traveling distance of the positive third lens group 30 becomeslonger to the extent that d_(X3)/fw exceeds the upper limit of condition(3), it is advantageous for achieving a higher zoom ratio; however, theoverall length of the wide-angle zoom lens system becomes longer, andthe amount of peripheral illumination decreases.

In the wide-angle zoom lens system of the present invention, uponzooming, the distance between the positive third lens group 30 and thenegative fourth lens group 40 is arranged to increase, and the distancebetween the negative fourth lens group 40 and the positive fifth lensgroup 50 is arranged to decrease. This movement of the lens groupsprovides an effect similar to one which can be obtained from aninner-focusing type lens system. Due to the above arrangement, an effectof zooming by the movement of the positive third lens group 30 to thepositive fifth lens group 50 is enhanced, so that a higher zoom rationcan be obtained.

In this case, if the positive third lens group 30 and the positive fifthlens group 50 are arranged to integrally move, the cam mechanism of thewide-angle zoom lens system can be simplified, and an error due todecentration can advantageously be reduced.

Particularly, in the wide-angle zoom lens system of the presentinvention, the bundle of light rays which is diverged from the negativefirst lens group 10 is collected by the positive third lens group 30through the positive fifth lens group 50 which have a strongerrefractive power than the negative first lens group 10 does, so thaterror sensitivity becomes high. If the positive third lens group 30 andthe positive fifth lens group 50 are made integral, i.e., madestructurally rigid, occurrence of an error due to decentration can bereduced.

In addition to the integral movement of the positive third lens group 30and the positive fifth lens group 50, if the positive third lens group30, the negative fourth lens group 40 and the positive fifth lens group50 are arranged to move linearly, the mechanism of the wide-angle zoomlens system can further be simplified, and the weight and cost of thewide-angle zoom lens system can be advantageously reduced.

In the embodiments of the present invention, for the purpose ofachieving (i) an angle-of-view of more than 100γ at the short focallength extremity, and (ii) a longer back focal distance, a strongnegative refractive power is necessary in the first lens group 10.Specifically, in order to distribute the strong negative refractivepower over a plurality of glass lens elements, of the negative firstlens group 10, having high refractive indexes, the negative first lensgroup 10 generally includes a negative first meniscus lens elementhaving the convex surface facing toward the object, a negative secondmeniscus lens element having the convex surface facing toward theobject, a negative third lens element (refer to the fourth embodimentdiscussed below), and a positive fourth lens element, in this order fromthe object. With the above arrangement, it is preferable that distortionoccurred under a storing negative refractive power be corrected by thepositive fourth lens element and aspherical surfaces provided on any ofthe diverging surfaces of the first through the third lens elements,e.g., the image-side concave surface of the negative first meniscus lenselement (also refer to the fourth embodiments).

However, since the diameter of the negative first lens group 10 isrelatively large, the manufacturing cost of the negative first lensgroup 10 made of high refractive glass becomes higher.

Furthermore, if an attempt is made to provide an aspherical surface onany of the lens surfaces, it would be possible to eliminate one negativelens element. However, the manufacturing costs of a glass-molded lenselement and a hybrid lens element are extremely high. This is because,(i) a glass-molded lens element is made by heating a special opticalglass, and by being press-molded with an aspherical-surface mold; and(ii) a hybrid lens element is made by bonding a thin resinaspherical-surface layer over a spherical glass lens element. Thereforean effect of cost-reduction by eliminating one glass lens element isalmost nullified.

Here, if a glass lens element is replaced with a resin aspherical lenselement which can easily be molded, a major cost-reduction is expectedwhile the optical performance of the resin aspherical lens element canbe maintained substantially the same as that of the glass lens element.

On the other hand, according to the above-explained arrangement of thenegative first lens group 10, the negative and positive lens elementshave strong refractive power, so that it is not practical to merelyreplace each of the above negative and positive lens elements withresin-molded lens elements. This is because a resin-molded lens elementis vulnerable to environmental changes, such as the changes intemperature and humidity. Then, it is preferable that one negative lenselement, which is made of optical glass and has a strong negativerefractive power, be divided into one negative lens element made ofoptical glass, and one aspherical lens element which is made of resinand has an extremely weak power. According to this arrangement, a majorcost-reduction can be made, while suitable optical performance ismaintained even when one negative lens element made of optical glass iseliminated from the negative first lens group 10.

More specifically, as the third lens element, a positive meniscus lenselement (refer to the first to third embodiments discussed below) havingthe convex surface facing toward the object can also be provided,instead of the negative third lens element (the fourth embodiment).Furthermore, in the case where the third positive meniscus lens elementis formed as the aspherical meniscus lens element made of resin, itbecomes possible to correct distortion with low cost.

Here, it goes without saying that optical performance can further beenhanced, if a negative lens element made of optical glass isincorporated in addition to the resin-molded aspherical third lenselement satisfying Condition (4), though the cost will become higher(refer to the second embodiment discussed below).

Condition (4) specifies the refractive power of the above-explainedthird lens element.

If the absolute value of the refractive power becomes stronger to theextent that |f1/f_(L3)| exceeds the (upper) limit of condition (4), anin-focus state and aberrations would undesirably be changed due to theenvironmental changes, such as a change in temperature, etc.Consequently, it becomes substantially impractical to make the thirdlens element from resin.

In the negative first lens group 10, the two negative lens elements onthe side of the object are necessary to make the angle-of-view at theshort focal length extremity larger, and to secure a longer back focaldistance. However, distortion occurs in these two negative lenselements. Therefore if an attempt is made to reduce distortion under thecondition that (i) the diameter of the negative first lens group 10 ismaintained smaller, and (ii) the negative first lens group 10 isconstituted by fewer lens elements, it is preferable that at least onesurface of the two negative lens elements be provided with an asphericalsurface.

Specifically, at least one surface mentioned above is preferably formedas a hybrid aspherical surface.

In addition, in the case where the third lens element is formed as aresin-molded aspherical lens element which has a weak refractive powerso as to satisfy Condition (4), the negative first lens group 10 can beformed as an optical system which is inexpensive and maintains suitableoptical performance.

Condition (5) specifies the refractive power of the positive third lensgroup 30.

If the refractive power of the positive third lens group 30 becomesweaker to the extent that fw/f3 exceeds the lower limit of condition(5), the overall length of the wide-angle zoom lens system becomeslonger, so that the height of light rays incident on the negative fourthlens group 40 becomes higher. Consequently, spherical aberration in thepositive direction occurs at the long focal length extremity.

If the refractive power of the positive third lens group 30 becomesstronger to the extent that fw/f3 exceeds the upper limit of condition(5), it is advantageous to reduce the overall length of the wide-anglezoom lens system; however, strong spherical aberration in the negativedirection occurs, and, in particular, the balance of aberrations on theentire wide-angle zoom lens system cannot be maintained at the shortfocal length extremity.

Condition (6) specifies the refractive power of the negative fourth lensgroup 40.

If the refractive power of the negative fourth lens group 40 becomesweaker to the extent that fw/f4 exceeds the lower limit of condition(6), the traveling distance of the negative fourth lens group 40 becomeslonger to obtain a higher zoom ratio, so that the size of the wide-anglezoom lens system becomes larger.

If the refractive power of the negative fourth lens group 40 becomesstronger to the extent that fw/f4 exceeds the upper limit of condition(6), the diameter of the positive fifth lens group 50 becomes larger,and strong spherical aberration in the positive direction occurs.Moreover, the balance of aberrations on the entire wide-angle zoom lenssystem cannot be maintained.

Specific numerical data of the embodiments will be describedhereinafter.

In the diagrams showing spherical aberration and the sine condition, SAdesignates spherical aberration, and SC designates the sine condition.

In the diagrams of chromatic aberration represented by sphericalaberration, the solid line and the two types of dotted linesrespectively indicate spherical aberrations with respect to the d, g andC lines.

In the diagrams of lateral chromatic aberration, the two types of dottedlines respectively indicate magnification with respect to the 9 and Clines; however, the d line as the base line coincides with the ordinate.

In the diagrams of astigmatism, S designates the sagittal image, and Mdesignates the meridional image.

In the tables, F_(NO) designates the f-number, f designates the focallength of the entire wide-angle lens system, f_(B) designates the backfocal distance (the equivalent air thickness along the optical axis fromthe most image-side surface of the positive fifth lens group 50 to theimage plane), w designates the half angle-of-view (*), r designates theradius of curvature, d designates the lens-element thickness or distancebetween lens elements, N_(d) designates the refractive index of thed-line, and ! designates the Abbe number.

In addition to the above, an aspherical surface which is symmetricalwith respect to the optical axis is defined as follows:x=cy ²/(1+[1−{1+K}c ² y ²]^(1/2))+A4y ⁴ +A6y ⁸ +A10y ¹⁰

-   -   wherein:    -   c designates a curvature of the aspherical vertex (1/r);    -   y designates a distance from the optical axis;    -   K designates the conic coefficient;    -   A4 designates a fourth-order aspherical coefficient;    -   A6 designates a sixth-order aspherical coefficient;    -   A8 designates a eighth-order aspherical coefficient; and    -   A10 designates a tenth-order aspherical coefficient.        [Embodiment 1]

FIG. 1 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity according to the first embodiment of thepresent invention. FIGS. 2A through 2E show aberrations occurred in thelens arrangement shown in FIG. 1. FIGS. 3A through 3E show aberrationsoccurred in the lens arrangement shown in FIG. 1 at an intermediatefocal length (24.00) on the side of the shorter focal length. FIGS. 4Athrough 4E show aberrations occurred in the lens arrangement shown inFIG. 1 at an intermediate focal length (35.00) on the side of the longerfocal length. FIGS. 5A through 5E show aberrations occurred in the lensarrangement shown in FIG. 1 at the long focal length extremity. Table 1shows the numerical data of the first embodiment.

The negative first lens group 10 includes a negative meniscus lenselement 11 having the convex surface facing toward the object, anegative meniscus lens element 12 having the convex surface facingtoward the object, a positive meniscus lens element 13, with a weakrefractive power, having the convex surface facing toward the object,and a positive meniscus lens element 14 having the convex surface facingtoward the object, in this order from the object.

The positive second lens group 20 includes cemented lens elements havinga biconvex positive lens element 21 and a negative lens element 22, inthis order from the object.

The positive third lens group 30 includes a positive lens element 31,cemented lens elements having a biconvex positive lens element 32 and anegative lens element 33, in this order from the object.

The negative fourth lens group 40 includes cemented lens elements havinga positive lens element 41 and a negative lens element 42, in this orderfrom the object.

The positive fifth lens group 50 includes a positive lens element 51, anegative lens element 52, and a negative meniscus lens element 53 havingthe convex surface facing toward the image, in this order from theobject.

In the negative first lens group 10, the concave surface of the mostobject-side negative meniscus lens element 11 is an aspherical surfaceformed by bonding a thin resin layer; and the positive meniscus lenselement 13, with a weak refractive power, having the convex surfacefacing toward the object is an aspherical lens element made of resin.

Furthermore, in the positive fifth lens group 50, the most object-sidepositive lens element 51 is an aspherical lens element made of resin.

The diaphragm S is provided at 1.70 on the object side of the positivethird lens group 30 (in front of surface No. 12).

TABLE 1 FNO. = 1:3.4-3.7-4.5-5.8 f = 18.60-24.00-35.00-53.35 W =50.8-42.6-31.7-21.9 f_(B) = 36.99-43.61-55.72-74.22 Surf. No. r d Nd    !  1 282.135 1.60 1.71300 / 53.9  2 23.418 0.20 1.52700 / 43.7(resin)  3* 17.581 8.94  4 102.770 1.60 1.69680 / 55.5  5 29.830 0.10 6* 20.830 2.20 1.52538 / 56.3 (resin)  7* 21.503 4.49  8 51.142 3.901.84666 / 23.8  9 147.819 31.58-19.45-8.61-1.40 10 42.416 4.40 1.60342 /38.0 11 −32.595 1.60 1.80610 / 40.9 12 −441.748 16.25-12.52-6.26-3.10 1378.284 2.98 1.51742 / 52.4 14 −48.704 0.10 15 30.798 4.46 1.51742 / 52.416 −37.106 1.30 1.84666 / 23.8 17 174.350 1.66-3.99-8.26-14.76 18909.325 3.04 1.69895 / 30.1 19 −39.452 1.30 1.79952 / 42.2 20 57.04415.40-13.07-8.81-2.30  21* −3344.056 4.55 1.52538 / 56.3 (resin) 2221.541 0.10 23 790.017 2.01 1.55963 / 61.2 24 886.113 1.98 25 −41.5561.50 1.84666 / 23.9 26 −72.183 − *designates the aspherical surfacewhich is rotationally symmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)):

Surf. No. K A4 3 −0.10000 × 10 −0.11630 × 10⁻⁶ 6 −0.10000 × 10 −0.28609× 10⁻⁵ 7 −0.10000 × 10 −0.95796 × 10⁻⁵ 21  −0.10000 × 10 −0.20968 × 10⁻⁴Surf. No. A6 A8 3 −0.18732 × 10⁻⁷  0.30062 × 10⁻¹⁰ 6 −0.26403 × 10⁻⁷ 0.71114 × 10⁻¹⁰ 7 −0.21000 × 10⁻⁷  0.48454 × 10⁻¹⁰ 21  −0.22282 × 10⁻⁷ 0.54838 × 10⁻¹⁰[Embodiment 2]

FIG. 6 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity according to the second embodiment of thepresent invention. FIGS. 7A through 7E show aberrations occurred in thelens arrangement shown in FIG. 6. FIGS. 8A through 8E show aberrationsoccurred in the lens arrangement shown in FIG. 6 at an intermediatefocal length (24.00) on the side of the shorter focal length. FIGS. 9Athrough 9E show aberrations occurred in the lens arrangement shown inFIG. 6 at an intermediate focal length (35.04) on the side of the longerfocal length. FIGS. 10A through 10E show aberrations occurred in thelens arrangement shown in FIG. 6 at the long focal length extremity.Table 2 shows the numerical data of the second embodiment.

The negative first lens group 10 includes a negative meniscus lenselement 11 having the convex surface facing toward the object, anegative meniscus lens element 12 having the convex surface facingtoward the object, a positive meniscus lens element 13, with a weakrefractive power, having the convex surface facing toward the object, abiconcave negative lens element 14, and a positive meniscus lens element15 having the convex surface facing toward the object, in this orderfrom the object.

The positive fifth lens group 50 includes a positive lens element 51, apositive lens element 52, and a biconcave negative lens element 53, inthis order from the object.

In the negative first lens group 10, the concave surface of the mostobject-side negative meniscus lens element 11 is an aspherical surfaceformed by bonding a thin resin layer; and the positive meniscus lenselement 13, with a weak refractive power, having the convex surfacefacing toward the object is an aspherical lens element made of resin.

Furthermore, in the positive fifth lens group 50, the object-sidesurface of the most object-side positive lens element 51 is anaspherical surface formed by bonding a thin resin layer.

The basic arrangements of the positive second lens group 20, thepositive third lens group 30 and the negative fourth lens group 40 arethe same as those of the first embodiment.

The diaphragm S is provided at 1.70 on the object side of the positivethird lens group 30 (in front of surface No.12).

TABLE 2 FNO. = 1:3.3-3.7-4.4-5.8 f = 18.60-24.00-35.04-53.34 W =50.8-42.7-31.5-21.7 f_(B) = 38.09-46.29-58.18-76.76 Surf. No. r d Nd    !  1 79.276 1.60 1.80400 / 46.6  2 22.879 0.30 1.52700 / 43.7(resin)  3* 18.377 5.75  4 42.505 1.60 1.77250 / 49.6  5 22.746 0.86  620.801 2.50 1.52538 / 56.3 (resin)  7* 24.676 8.35  8 −71.771 1.501.69680 / 55.5  9 71.771 0.16 10 46.627 4.10 1.84666 / 23.8 11 761.05815.54-12.31-6.86-1.51 12 69.053 5.04 1.59551 / 39.2 13 −23.456 1.601.83400 / 37.2 14 −89.400 26.18-12.56-4.39-3.10 15 49.460 4.14 1.51633 /64.1 16 −36.708 0.20 17 43.573 5.11 1.51633 / 64.1 18 −25.073 1.301.85026 / 32.3 19 −1098.297 2.39-2.52-7.50-15.49 20 −59.457 3.14 1.84666/ 23.8 21 −25.425 1.30 1.78590 / 44.2 22 135.314 15.40-15.27-10.28-2.30 23* −2678.694 0.30 1.52700 / 43.7 (resin) 24 −113.799 5.42 1.55963 /61.2 25 −23.286 0.10 26 99.154 6.53 1.51633 / 64.1 27 −28.885 1.03 28−43.520 1.50 1.85026 / 32.3 29 62.884 — *designates the asphericalsurface which is rotationally symmetrical with respect to the opticalaxis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)):

Surf. No. K A4 3 −0.10000 × 10  0.83218 × 10⁻⁶ 7 −0.10000 × 10  0.86049× 10⁻⁵ 23  −0.10000 × 10 −0.28311 × 10⁻⁴ Surf. No. A6 A8 3  0.18285 ×10⁻⁷ −0.54982 × 10⁻¹⁰ 7 −0.23086 × 10⁻⁷  0.11096 × 10⁻⁹ 23  −0.34547 ×10⁻⁸ −0.32575 × 10⁻¹⁰[Embodiment 3]

FIG. 11 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity according to the third embodiment of thepresent invention. FIGS. 12A through 12E show aberrations occurred inthe lens arrangement shown in FIG. 11. FIGS. 13A through 13E showaberrations occurred in the lens arrangement shown in FIG. 11 at anintermediate focal length (23.98) on the side of the shorter focallength. FIGS. 14A through 14E show aberrations occurred in the lensarrangement shown in FIG. 11 at an intermediate focal length on the sideof the longer focal length. FIGS. 15A through 15E show aberrationsoccurred in the lens arrangement shown in FIG. 11 at the long focallength extremity. Table 3 shows the numerical data of the thirdembodiment.

The positive fifth lens group 50 includes a resin-molded positive lenselement 51, and cemented lens elements having a negative lens element 52and a positive lens element 53, in this order from the object.

The basic arrangements of the negative first lens group 10, the positivesecond lens group 20, the positive third lens group 30 and the negativefourth lens group 40 are the same as those of the first embodiment.

The diaphragms is provided at 1.70 on the object side of the positivethird lens group 30 (in front of surface No.12).

TABLE 3 FNO. = 1:3.4-3.8-4.5-5.8 f = 18.60-23.98-35.00-53.341 W =50.8-42.4-31.5-21.8 f_(B) = 37.00-43.38-55.01-72.79 Surf. No. r d Nd    !  1 240.793 1.60 1.69680 / 55.5  2 23.713 0.20 1.52700 / 43.7(resin)  3* 18.002 9.06  4 102.026 1.60 1.69680 / 55.5  5 30.476 0.10 6* 20.304 2.20 1.52538 / 56.3 (resin)  7* 20.376 5.86  8 55.499 3.621.84666 / 23.8  9 146.313 31.71-19.36-8.66-1.40 10 44.245 4.24 1.60342 /38.0 11 −39.732 1.60 1.80610 / 40.9 12 7212.805 18.69-14.75-7.38-3.10 1390.075 3.19 1.51742 / 52.4 14 −39.962 0.10 15 31.139 4.46 1.51742 / 52.416 −36.601 1.30 1.84666 / 23.8 17 222.957 1.79-4.12-8.38-14.68 18−375.317 2.99 1.69895 / 30.1 19 −23.206 1.30 1.79952 / 42.2 20 89.08815.40-13.06-8.81-2.30  21* 119.292 4.48 1.52538 / 56.3 (resin) 22−25.697 0.10 23 −5632.116 1.50 1.83400 / 37.2 24 24.364 5.32 1.51742 /52.4 25 −265.456 − *designates the aspherical surface which isrotationally symmetrical with respect to the optical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)):

Surf. No. K A4 3 −0.10000 × 10  0.29563 × 10⁻⁵ 6 −0.10000 × 10 −0.23265× 10⁻⁵ 7 −0.10000 × 10 −0.86218 × 10⁻⁵ 21  −0.10000 × 10 −0.18068 × 10⁻⁴Surf. No. A6 A8 3 −0.17807 × 10⁻⁷  0.13876 × 10⁻¹⁰ 6 −0.28621 × 10⁻⁷ 0.11896 × 10⁻⁹ 7 −0.17031 × 10⁻⁷  0.10722 × 10⁻⁹ 21   0.11262 × 10⁻⁷ 0.67757 × 10⁻¹⁰[Embodiment 4]

FIG. 16 is a lens arrangement of the wide-angel zoom lens system at theshort focal length extremity according to the fourth embodiment of thepresent invention. FIGS. 17A through 17E show aberrations occurred inthe is lens arrangement shown in FIG. 16. Figures 18A through 18E showaberrations occurred in the lens arrangement shown in FIG. 16 at anintermediate focal length (24.00) on the side of the shorter focallength. FIGS. 19A through 19E show aberrations occurred in the lensarrangement shown in FIG. 16 at an intermediate focal length (35.04) onthe side of the longer focal length. FIGS. 20A through 20E showaberrations occurred in the lens arrangement shown in FIG. 16 at thelong focal length extremity. Table 4 shows the numerical data of thefourth embodiment.

The negative first lens group 10 includes a negative meniscus lenselement 11 having the convex surface facing toward the object, anegative meniscus lens element 12 having the convex surface facingtoward the object, a biconcave negative lens element 13, and a positivemeniscus lens element 14 having the convex surface facing toward theobject, in this order from the object.

The positive fifth lens group 50 includes a positive lens element 51,and cemented lens elements having a negative lens element 52 and apositive lens element 53, in this order from the object.

In the negative first lens group 10, the concave surface of the mostobject-side negative meniscus lens element 11 is an aspherical surfaceformed by bonding a thin resin layer; and the biconcave negative lenselement 13 is made of glass.

Furthermore, in the positive fifth lens group 50, the object-sidesurface of the most object-side positive lens element 51 is anaspherical surface formed by bonding a thin resin layer.

The diaphragms is provided at 1.70 on the object side of the positivethird lens group 30 (in front of surface No.12).

TABLE 4 FNO. = 1:3.5-3.8-4.5-5.8 f = 18.60-24.00-35.00-53.34 W =50.8-42.3-31.1-21.5 f_(B) = 39.38-48.08-59.74-74.51 Surf. No. r d Nd    !  1 71.009 1.60 1.80400 / 46.6  2 21.734 0.30 1.52700 / 43.7(resin)  3* 17.586 6.40  4 41.805 1.60 1.77250 / 49.6  5 25.044 7.89  6−82.736 1.50 1.69680 / 55.5 (glass)  7 82.736 0.12  8 41.175 4.161.84666 / 23.8  9 196.553 18.61-15.12-8.93-1.52 10 67.632 4.64 1.56732 /42.8 11 −24.451 1.60 1.80610 / 40.9 12 −97.694 27.54-13.60-3.92-3.10 1361.623 4.31 1.51633 / 64.1 14 −31.194 0.20 15 35.960 5.18 1.51633 / 64.116 −23.330 1.30 1.80610 / 33.3 17 −539.305 2.44-2.45-6.47-15.53 18−66.396 2.40 1.80518 / 25.4 19 −28.215 1.30 1.77250 / 49.6 20 92.93915.40-15.38-11.37-2.30  21* 153.678 0.30 1.52700 / 43.7 (resin) 22−118.608 5.68 1.65160 / 58.5 23 −21.850 1.61 24 −98.915 1.50 1.83400 /37.2 25 28.490 6.35 1.56384 / 60.7 26 −88.596 — *designates theaspherical surface which is rotationally symmetrical with respect to theoptical axis.

Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)):

Surf. No. K A4 3 −0.10000 × 10  0.25448 × 10⁻⁵ 21  −0.10000 × 10−0.25469 × 10⁻⁴ Surf. No. A6 A8 3  0.87109 × 10⁻⁸ −0.25017 × 10⁻¹⁰ 21  0.31819 × 10⁻⁸ −0.10737 × 10⁻¹⁰

Table 5 shows the numerical values for each condition in eachembodiment.

TABLE 5 Embod. 1 Embod. 2 Embod. 3 Embod. 4 Cond. (1) 2.295 0.608 1.9440.699 Cond. (2) 2.480 2.152 2.619 2.390 Cond. (3) 2.002 2.079 1.9241.889 Cond. (4) 0.042 0.101 0.026 Cond. (5) 0.401 0.464 0.441 0.545Cond. (6) −0.294 −0.331 −0.284 −0.362

In Table 5, no numerical value of condition (4) for the fourthembodiment is indicated, since a meniscus lens element having the convexsurface facing toward the object is not provided in the fourthembodiment.

Except for the above numerical value of condition (4) in the fourthembodiment, the numerical values of the first through fourth embodimentssatisfy the conditions (1) through (6). Furthermore, as shown in theaberration drawings, the various aberrations are adequately corrected.

According to the above description, a wide-angle zoom lens system, inwhich (i) the angle-of-view of at the short focal length extremity ismore than 100γ, (ii) a zoom ratio is approximately 2.9, and (iii) thediameter of lens elements is smaller, can be achieved.

1. A wide-angle zoom lens system comprising a negative first lens group,a positive second lens group, a positive third lens group, a negativefourth lens group, and a positive fifth lens group, in this order froman object; wherein upon zooming from the short focal length extremity tothe long focal length extremity, said negative first lens group firstmoves toward an image and thereafter moves toward said object, thedistance between said negative first lens group and said positive secondlens group decreases, the distance between said positive second lensgroup and said positive third lens group decreases, the distance betweensaid positive third lens group and said negative fourth lens groupincreases, and the distance between said negative fourth lens group andsaid positive fifth lens group decreases; wherein said wide-angle zoomlens system satisfies the following conditions:0.3<dL ₁₋₂/dL₂₋₃<5.02.1<(L _(t-2) +L ₂₋₃)/fW<5.5 wherein dL₁₋₂ designates the difference inthe distance between said negative first lens group and said positivesecond lens group at the short focal length extremity and the distancetherebetween at the long focal length extremity; dL₂₋₃ designates thedifference in the distance between said positive second lens group andsaid positive third lens group at the short focal length extremity andthe distance therebetween at the long focal length extremity; L₁₋₂designates the distance between said negative first lens group and saidpositive second lens group at the short focal length extremity: ₂₋₃designates the distance between said positive third lens group and saidnegative fourth lens group at the short focal length extremity; and fwdesignates the focal length of said entire wide-angle zoom lens systemat the short focal length extremity.
 2. The wide-angle zoom lens systemaccording to claim 1, wherein said positive third lens group and saidpositive fifth lens group are arranged to move integrally upon zooming.3. The wide-angle zoom lens system according to claim 1, furthersatisfying the following condition: 1.7<d _(X3) /fw<4.0 wherein d_(X3)designates the traveling distance of said positive third lens group fromthe short focal length extremity to the long focal length extremity; andfw designates the focal length of said entire wide-angle zoom lenssystem at the short focal length extremity.
 4. The wide-angle zoom lenssystem according to claim 1, wherein said positive third lens group andsaid negative fourth lens group are arranged to move linearly uponzooming.
 5. The wide-angle zoom lens system according to claim 1,wherein said negative first lens group comprises a negative firstmeniscus lens element having the convex surface facing toward saidobject, a negative second meniscus lens element having the convexsurface facing toward said object, and a third meniscus lens elementhaving the convex surface facing toward said object, in this order fromsaid object, wherein said third meniscus lens element is made of resin;and wherein said negative first lens group satisfies the followingcondition:|f1/f _(L3|<)0.2 wherein f1 designates the focal length of said negativefirst lens group; and f_(L3) designates the focal length of said thirdmeniscus lens element in said negative first lens group.
 6. Thewide-angle zoom lens system according to claim 1, further satisfying thefollowing condition:0.2<fw/f3<0.9 wherein designates the focal length of said positive thirdlens group; and fw designates the focal length of said entire wide-anglezoom lens system at the short focal length extremity.
 7. The wide-anglezoom lens system according to claim 1, further satisfying the followingcondition:<0.6<fw/f4<−0.1 wherein f4 designates the focal length of said negativefourth lens group; and fw designates the focal length of said entirewide-angle zoom lens system at the short focal length extremity.
 8. Awide-angle zoom lens system comprising a negative first lens group, apositive second lens group, a positive third lens group, a negativefourth lens group, and a positive fifth lens group, in this order froman object, wherein said positive third lens group and said positivefifth lens group are arranged to move integrally upon zooming; whereinupon zooming from the short focal length extremity to the long focallength extremity, said negative first lens group first moves toward animage and thereafter moves toward said object, the distance between saidnegative first lens group and said positive second lens group decreases,the distance between said positive second lens group and said positivethird lens group decreases, the distance between said positive thirdlens group and said negative fourth lens group increases, and thedistance between said negative fourth lens group and said positive fifthlens group decreases; wherein said wide-angle zoom lens system satisfiesthe following condition:0.3<dL ₁₋₂ /dL _(2-3<)5.0 wherein dL₁₋₂ designates the difference in thedistance between said negative first lens group and said positive secondlens group at the short focal length extremity and the distancetherebetween at the long focal length extremity; and dL₂₋₃ designatesthe difference in the distance between said positive second lens groupand said positive third lens group at the short focal length extremityand the distance therebetween at the long focal length extremity.
 9. Thewide-angle zoom lens system according to claim 8, further satisfying thefollowing condition:1.7<d _(X3) fw<4.0 wherein d_(X3) designates the traveling distance ofsaid positive third lens group from the short focal length extremity tothe long focal length extremity; and fw designates the focal length ofsaid entire wide-angle zoom lens system at the short focal lengthextremity.
 10. The wide-angle zoom lens system according to claim 8,wherein said positive third lens group and said negative fourth lensgroup are arranged to move linearly upon zooming.
 11. The wide-anglezoom lens system according to claim 8, wherein said negative first lensgroup comprises a negative first meniscus lens element having the convexsurface facing toward said object, a negative second meniscus lenselement having the convex surface facing toward said object, and a thirdmeniscus lens element having the convex surface facing toward saidobject, in this order from said object, wherein said third meniscus lenselement is made of resin; and wherein said negative first lens groupsatisfies the following condition:|f1/f _(L3)|<0.2 wherein f1 designates the focal length of said negativefirst lens group; and f_(L3) designates the focal length of said thirdmeniscus lens element in said negative first lens group.
 12. Thewide-angle zoom lens system according to claim 8, further satisfying thefollowing condition:0.2<fw/f3<0.9 wherein f3 designates the focal length of said positivethird lens group; and fw designates the focal length of said entirewide-angle zoom lens system at the short focal length extremity.
 13. Thewide-angle zoom lens system according to claim 8, further satisfying thefollowing condition: ti −0.6<fw/f4<−0.1 wherein f4 designates the focallength of said negative fourth lens group; and fw designates the focallength of said entire wide-angle zoom lens system at the short focallength extremity.
 14. A wide-angle zoom lens system comprising anegative first lens group, a positive second lens group, a positivethird lens group, a negative fourth lens group, and a positive fifthlens group, in this order from an object, wherein said positive thirdlens group and said negative fourth lens group are arranged to movelinearly upon zooming, wherein upon zooming from the short focal lengthextremity to the long focal length extremity, said negative first lensgroup first moves toward an image and thereafter moves toward saidobject, the distance between said negative first lens group and saidpositive second lens group decreases, the distance between said positivesecond lens group and said positive third lens group decreases, thedistance between said positive third lens group and said negative fourthlens group increases, and the distance between said negative fourth lensgroup and said positive fifth lens group decreases; wherein saidwide-angle zoom lens system satisfies the following condition:0.3<dL ₁₋₂ /dL ₂₋₃<5.0 wherein dL₁₋₂ designates the difference in thedistance between said negative first lens group and said positive secondlens group at the short focal length extremity and the distancetherebetween at the long focal length extremity; and dL₂₋₃ designatesthe difference in the distance between said positive second lens groupand said positive third lens group at the short focal length extremityand the distance therebetween at the long focal length extremity. 15.The wide-angle zoom lens system according to claim 14, furthersatisfying the following condition:1.7<d _(X3)/fw<4.0 wherein d_(X3) designates the traveling distance ofsaid positive third lens group from the short focal length extremity tothe long focal length extremity; and fw designates the focal length ofsaid entire wide-angle zoom lens system at the short focal lengthextremity.
 16. The wide-angle zoom lens system according to claim 14,wherein said negative first lens group comprises a negative firstmeniscus lens element having the convex surface facing toward saidobject, a negative second meniscus lens element having the convexsurface facing toward said object, and a third meniscus lens elementhaving the convex surface facing toward said object, in this order fromsaid object, wherein said third meniscus lens element is made of resin;and wherein said negative first lens group satisfies the followingcondition:|f1/f _(L3)|<0.2 wherein f1 designates the focal length of said negativefirst lens group; and f_(L3) designates the focal length of said thirdmeniscus lens element in said negative first lens group.
 17. Thewide-angle zoom lens system according to claim 14, further satisfyingthe following condition:0.2<fw/f3<0.9 wherein f3 designates the focal length of said positivethird lens group; and fw designates the focal length of said entirewide-angle zoom lens system at the short focal length extremity.
 18. Thewide-angle zoom lens system according to claim 14, further satisfyingthe following condition:−0.6<fw/f4<−0.1 f4 designates the focal length of said negative fourthlens group; and fw designates the focal length of said entire wide-anglezoom lens system at the short focal length extremity.